Beamforming by antenna puncturing

ABSTRACT

Beamforming is provided for a wireless MIMO device by using antenna puncturing to reduce the number of transmit antennas that are used to transmit data for certain subcarriers. In a conventional approach, if N spatial streams are being used to provide spatial multiplexing, then N transmit antennas would be used to transmit for each subcarrier. In at least one embodiment of the invention, enhancements in channel capacity are achieved by using less than N transmit antennas for one or more subcarriers.

TECHNICAL FIELD

The invention relates generally to electronic communication and, moreparticularly, to techniques for performing beamforming in communicationsystems systems.

BACKGROUND OF THE INVENTION

Multiple input, multiple output (MIMO) is a communication technique thatuses multiple antennas (or other transducers) at each end of acommunication channel. For example, multiple transmit antennas may beused to transmit signals into a wireless channel and multiple receiveantennas may be used to receive signals at the other end of the channel.MIMO technology is capable of providing improved spectral efficiency inthe channel by providing benefits such as array gain, diversity gain,and increased co-channel interference rejection. These benefits can beused to provide increases in data rate, communication range,reliability, number of users services, and/or other operationalparameters. Multicarrier communication is a technique that uses a numberof relatively narrowband subchannels to transmit data from one point toanother. Multicarrier technologies, such as orthogonal frequencydivision multiplexing (OFDM), can be used to provide resistance tointersymbol interference (ISI) and other harmful channel effects.Strategies are needed for efficiently implementing multicarriercommunication techniques within MIMO based systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example wireless networkarrangement that may incorporate features of the present invention;

FIGS. 2, 3, and 4 are diagrams illustrating the difference betweentraditional antenna selection and antenna puncturing in accordance withan embodiment of the present invention;

FIG. 5 is a block diagram illustrating an example transmitter system inaccordance with an embodiment of the present invention;

FIG. 6 is a block diagram illustrating example antenna puncture logicthat can be used to perform antenna puncturing within a transmittersystem for a single subcarrier in accordance with an embodiment of thepresent invention;

FIG. 7 is a block diagram illustrating another example transmittersystem that can be used in accordance with an embodiment of the presentinvention;

FIG. 8 is a block diagram illustrating an example antenna switcharrangement in accordance with an embodiment of the present invention;and

FIG. 9 is a flowchart illustrating an example method for performingantenna puncturing in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, specificembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention. It is to be understood that the variousembodiments of the invention, although different, are not necessarilymutually exclusive. For example, a particular feature, structure, orcharacteristic described herein in connection with one embodiment may beimplemented within other embodiments without departing from the spiritand scope of the invention. In addition, it is to be understood that thelocation or arrangement of individual elements within each disclosedembodiment may be modified without departing from the spirit and scopeof the invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined only by the appended claims, appropriately interpreted, alongwith the full range of equivalents to which the claims are entitled. Inthe drawings, like numerals refer to the same or similar functionalitythroughout the several views.

FIG. 1 is a block diagram illustrating an example wireless networkarrangement 10 that may incorporate features of the present invention.As shown, a transmitting device 12 is communicating with a receivingdevice 14 via a wireless channel. The transmitting device 12 and thereceiving device 14 both include multiple antennas. For example, in theillustrated embodiment, the transmitting device 12 includes threetransmit antennas 16 and the receiving device 14 includes two receiveantennas 18. In other embodiments, different numbers of antennas may beused. Any type of antennas may be used including, for example, dipoles,patches, helical antennas, and/or others. Because both the transmittingdevice 12 and the receiving device 14 have multiple antennas, multipleinput, multiple output (MIMO) techniques may be used to transmit datathrough the wireless channel. When MIMO is used, the wireless channelmay be referred to as a MIMO channel. The transmitting device 12 and thereceiving device 14 may each be associated with any type of device orsystem that is capable of communicating wirelessly. This may include,for example, a laptop, palmtop, desktop, or tablet computer havingwireless networking capability, a personal digital assistant (PDA)having wireless networking capability, a cellular telephone or otherhandheld wireless communicator, a wireless base station or access point,a wireless network client device, a satellite communicator, atransceiver within a communication satellite, a transceiver associatedwith a terrestrial wireless link, an ultra-mobile personal computer(UMPC), a pager, and/or other devices or systems.

In one MIMO technique, known as spatial multiplexing, input data issplit into N spatial streams before transmission (where N is a positiveinteger greater than 1). Data from the N spatial streams may then beindependently and simultaneously transmitted into the MIMO channel usingN transmit antennas. The receiver at the other side of the MIMO channelis then able to de-multiplex the N spatial streams as long as the numberof receive antennas is greater than or equal to the number of transmitantennas. The receiving device may include, for example, a maximumlikelihood (ML) receiver, a zero-forcing receiver, a minimum mean squareerror (MMSE) receiver, and/or some other, type of receiver for use inrecovering the transmitted data. Because an independent symbol stream istransmitted by each antenna, spatial multiplexing can achieve relativelyhigh throughput in a MIMO channel.

Multicarrier communication is a technique that uses a plurality ofsubcarriers to transmit data, in parallel, through a channel. One formof multicarrier communication that is presently very popular isorthogonal frequency division multiplexing (OFDM), which uses multipleorthogonal subcarriers to transmit data through a channel. Other formsof multicarrier communication also exist. In one aspect of the presentinvention, techniques are provided for improving performance in MIMOsystems that use multicarrier communication techniques.

Antenna selection is a technique that may be used within a MIMO-enableddevice or network to select less than an available number of antennasfor active communication. When spatial multiplexing is being used in aMIMO channel, one transmit antenna is typically used for each spatialstream. Thus, when antenna selection is implemented alongside spatialmultiplexing, the number of antennas that are selected is made equal tothe number of spatial streams being used. In conceiving the presentinvention, it was determined that additional capacity gains can beachieved by loosening the constraint on the number of transmit antennasto allow further reduction in the number of antennas used to performspatial multiplexing, on a subcarrier by subcarrier basis. Thistechnique is referred to herein as “antenna puncturing.” Antennapuncturing recognizes that, for some sub carriers, using a number ofantennas that is less than the number of spatial streams' can result ina higher overall capacity for the corresponding MIMO channel.

FIGS. 2, 3, and 4 are diagrams illustrating the difference betweentraditional antenna selection and antenna puncturing in accordance withan embodiment of the present invention. Each of these figures representsa transmission scenario at a particular transmit time within amulticarrier MIMO system that uses nine sub-carriers (represented asrows) and where there are three available transmit antennas (representedas columns). Crosshatching is used in the figures to identify antennasthat are active for a particular subcarrier. FIGS. 2 and 3 illustratethe use of antenna selection in a spatial multiplexing arrangement thatuses two spatial streams. In the example shown in FIG. 2, an antennaselection process is used that selects the same two antennas for each ofthe subcarriers (i.e., subcarriers 0-8). In the example of FIG. 3, anantenna selection process is used that can select a different set of twoantennas for each of the subcarriers.

In both FIG. 2 and FIG. 3, the number of antennas selected for eachsubcarrier is equal to the number of spatial streams. That is, for eachsubcarrier, one antenna is selected for each spatial stream.

FIG. 4 illustrates an example use of antenna puncturing for a MIMOchannel that uses spatial multiplexing with three spatial streams inaccordance with an embodiment of the present invention. As shown, adifferent number of active antennas may be selected for each subcarrierin the multicarrier band. For example, with reference to FIG. 4, threeantennas are active for subcarrier 0, two antennas are active forsubcarrier 1, three antennas are active for subcarrier 2, two antennasare active for subcarrier 3, and so on. Thus, the number of antennasthat are active for each subcarrier does not have to be equal to thenumber of spatial streams that are being used (i.e., it can be less).When the number of antennas that is used for a subcarrier is less thanthe number of spatial streams, one or more of the data symbolsassociated with that subcarrier is not transmitted (i.e., the symbol iserased). Another way to look at it is that these symbols are transmittedwith zero power. The erased symbols may be recovered in the receivingdevice using the error correction capabilities of the corresponding FECcode. Antenna puncturing is similar to the concept of code puncturing incoding where one or more code bits may be left out (or punctured) toadjust the rate of the code being used.

The purpose of antenna puncturing in a MIMO channel is typically toenhance some performance characteristic of the channel (e.g., channelcapacity). In one possible approach, the antenna puncturing computationsmay be carried out in a receiving device, using channel informationgenerated in the receiving device. The receiving device may then feedthe antenna puncture information back to the transmitting device for usein a subsequent transmission. In another possible approach, the antennapuncturing computations may be carried out in the transmitting deviceitself when channel information is available therein (e.g., if implicitor explicit feedback is used in a closed loop MIMO embodiment, etc.).Sometimes, when multiple antennas are transmitting at the same frequencywithin a common MIMO channel, one of the transmit antennas will cause alarge amount of interference for the other transmit antennas for aparticular subcarrier. Antenna puncturing can be used to prevent theinterference-causing antenna from transmitting for that subcarrier,thereby reducing interference and improving capacity. When a channelmatrix for a MIMO channel has two or more equal (or near equal) columns,then one of the transmit antennas being used may be aninterference-causing antenna as described above.

In general, antenna puncturing is a form of beamforming that may be usedto enhance the capacity of a MIMO channel. An optimal method ofbeamforming in a MIMO system is known as singular value decomposition(SVD) MIMO. When SVD techniques are used to perform beamforming, optimallevels of capacity enhancement can be achieved. However, SVD MIMOrequires a large amount of feedback to be transmitted from a receivingdevice to the transmitting device. At the opposite end of the spectrumis “spatial expansion” which requires no feedback, but providesrelatively little capacity enhancement. Antenna puncturing provides atradeoff between SVD MIMO and spatial expansion. That is, it provides anintermediate level of capacity enhancement while requiring a relativelysmall amount of feedback (i.e., when the antenna puncturingdeterminations are performed in the receiving device). In someembodiments, antenna puncturing may be implemented using only a few bitsof feedback per subcarrier. In a 3×3 MIMO implementation, this is aroundone twentieth the amount of feedback required by SVD. Antenna puncturingalso allows the error correcting codes to be confined to the same finiteset of rates and modulations used by antenna selection implementations.

When antenna puncturing information is computed within a receivingdevice and is fed back to the transmitting device, the receiving devicewill know where the puncturing is going to take place in the ensuingtransmission. This information may be used by the receiving device todecode the received information more reliably. The receiver may, forexample, avoid noise-only subcarriers by nulling them instead of tryingto determine which constellation point was transmitted.

FIG. 5 is a block diagram illustrating an example transmitter system 50in accordance with an embodiment of the present invention. As will bedescribed in greater detail, the transmitter system 50 is capable ofperforming antenna puncturing in a multicarrier, MIMO-based network. Itshould be appreciated that the transmitter of FIG. 5 is merely anexample of one type of architecture that may be used to perform antennapuncturing within a wireless device or system. Other transmitterarrangements may alternatively be used. As illustrated in FIG. 5, thetransmitter system 50 may include: a forward error correction (FEC)encoder 52; a spatial stream interleaver 54; first, second, and thirdsymbol generators 56, 58, 60; first, second, and thirdserial-to-parallel (S/P) converters 62, 64, 66; antenna puncture logic68; first, second, and third mapper/modulators (M/Ms) 70, 72, 74; first,second, and third inverse discrete Fourier transform (IDFT) units 76,78, 80; first, second, and third cyclic prefix (CP) inserters 82, 84,86; first, second, and third radio frequency (RF) transmitters 88, 90,92; and first, second, and third transmit antennas 94, 96, 98. The FECencoder 52 encodes an input bit stream using a predetermined errorcorrection code. The spatial stream interleaver 54 may then interleavethe serial stream of encoded bits into multiple spatial streams for usein providing spatial multiplexing. In the illustrated embodiment, thenumber of spatial streams generated by the spatial stream interleaver 54is three, which is also the number of available transmit antennas 94,96, 98. The number of spatial streams, the number of available transmitantennas, and the number of subcarriers per multicarrier symbol may varyfrom implementation to implementation.

The first, second, and third symbol generators 56, 58, 60 each receivethe encoded bits for a corresponding spatial stream and group the bitsinto symbols based on one or more modulation schemes. The S/P converters62, 64, 66 may each convert a serial stream of symbols associated with acorresponding spatial stream to a parallel representation associatedwith the subcarriers' of a multicarrier symbol (e.g., an OFDM symbol).Thus, each symbol will be associated with a subcarrier based on itslocation in the parallel representation. The antenna puncture logic 68may then apply antenna puncturing for the individual subcarriers of thespatial streams. As illustrated, the antenna puncture logic 68 mayperform the antenna puncturing in response to control information. Asdescribed previously, in some embodiments, the receiving device maygenerate the antenna puncture control information and feed it back tothe transmitting device. This feedback information (or a derivativethereof) may then be delivered to the antenna puncture logic 68. Inother embodiments, the antenna puncture control information may begenerated within the local device that is performing the puncturing (orelsewhere).

The antenna punctured data:output by the antenna puncture logic 68 isdirected to the M/Ms 70, 72, 74 which convert the bits of each symbol toconstellation points associated with the modulation scheme being used.The constellation points may then be used to modulate the correspondingdata subcarriers of the multicarrier symbol. Although not shown, pilotsymbols/tones will typically be added at some point in the processing.The modulated subcarriers for each spatial stream may next be deliveredto a corresponding IDFT 76, 78, 80 for conversion from a frequencydomain representation to a time domain representation. Any type of IDFTmay be used including, for example, an inverse fast Fourier transform(IFFT). The IDFTs 76, 78, 80 may apply a parallel-to-serial conversionto the time domain samples at an output thereof. The CP inserters 82,84, 86 each insert a cyclic prefix to a corresponding time domain signalto complete a multicarrier symbol. The multicarrier symbols may then bedirected to the corresponding RF transmitters 88, 90, 92 which convertthem from baseband signals to RF signals. The RF signals can then betransmitted from the corresponding antennas 94, 96, 98. The RFtransmitters 88, 90, 92 may each perform functions such as, for example,digital-to-analog conversion, up-conversion, signal amplification,signal filtration, and/or other functions commonly performed in an RFtransmitter.

FIG. 6 is a block diagram illustrating example antenna puncture logic100 that can be used to perform antenna puncturing within a transmittersystem in accordance with an embodiment of the present invention. Theantenna puncture logic 100 of FIG. 6 is for use with a singlesubcarrier. Separate antenna puncture logic 100 may be provided for eachsubcarrier or multiple subcarriers may share an antenna puncture logic100. In at least one embodiment, a single antenna puncture logic 100 isused for all of the subcarriers (e.g., one after another) in themulticarrier bandwidth. The antenna puncture logic 100 may also beimplemented in software. As shown in FIG. 6, the antenna puncture logic100 may receive one symbol from each spatial stream (i.e., symbol s₁from SS1, symbol s₂ from SS2, and symbol s₃ from SS3) that correspondsto a particular subcarrier. Based on control information, the antennapuncture logic 100 may replace one or more of the input symbols with azero or some other predetermined (dummy) symbol at a correspondingoutput. For instance, in the example of FIG. 6, the antenna puncturelogic 100 passes symbols s₁ and s₂ through to corresponding outputs, butreplaces symbol s₃ with a zero. With different control information,other puncture patterns can be achieved. In one possible approach, theantenna puncture logic 100 may perform the puncturing function bymultiplying a column vector of input symbols by a puncture matrix toachieve the output symbols, as follows:

$\begin{bmatrix}s_{1}^{\prime} \\s_{2}^{\prime} \\s_{3}^{\prime}\end{bmatrix} = {P \cdot \begin{bmatrix}s_{1} \\s_{2} \\s_{3}\end{bmatrix}}$

where P is the puncture matrix, S_(i) are the input symbols, and S_(i)are the output symbols. If there is no puncturing to be done for aparticular subcarrier, the puncture matrix may be, for example, theidentity matrix:

$P = \begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}$

If puncturing is to be performed, some possible puncture matrices mayinclude:

${P = \begin{bmatrix}1 & 0 & 0 \\0 & 0 & 0 \\0 & 0 & 1\end{bmatrix}},{P = \begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 0\end{bmatrix}},{P = \begin{bmatrix}0 & 0 & 0 \\0 & 0 & 1 \\0 & 1 & 0\end{bmatrix}},$

and so on. As described previously, any number of antennas may bepunctured for a particular subcarrier, except that at least one antennawill typically remain active for each subcarrier. In at least oneembodiment of the invention, the antenna puncture logic 100 may beimplemented as part of the mapper/modulators of a device (e.g., M/Ms 66,68, 70 in FIG. 5). For example, control signals may be delivered to themapper/modulators to control which antennas will transmit with zerotransmit power for each subcarrier. Other techniques for performing theantenna puncturing may alternatively be used.

In at least one embodiment of the present invention, the total transmitpower assigned to a subcarrier is maintained when antenna puncturing isbeing performed. In a typical scenario where N transmit antennas arebeing used for N spatial streams and the power assigned to a particularsubcarrier is P_(i), the power used for each antenna for that subcarrierwould be P_(i)/N. If antenna puncturing is used, then the power assignedto each active antenna may increase. For example, if L antennas areactive (L<N) for a subcarrier when antenna puncturing is being used,then the power assigned to each antenna may be P_(i)/L, which is greaterthan P_(i)/N. In some other embodiments, the power assigned to the Lselected antennas may remain the same as they would have been hadpuncturing not been used (i.e., P_(i)/N). Other transmit power schemesmay alternatively be used. In at least one embodiment, the power levelsfor each subcarrier are applied within the mapper/modulators (e.g., M/Ms66, 68, 70 in FIG. 5).

In the transmitter system 50 of FIG. 5, the number of spatial streams isequal to the number of available transmit antennas. FIG. 7 is a blockdiagram illustrating an example transmitter system 110 that can be usedto perform antenna puncturing when the number of available antennas isgreater than the number of spatial streams. As shown, the transmittersystem 110 generates three spatial streams, but has 5 available transmitantennas 114, 116, 118, 120, 122. In addition, the transmitter system110 includes a dedicated transmit chain 124 for each of the 5 availabletransmit antennas 114, 116, 118, 120, 122. The transmitter system 110includes beamforming logic 112 to perform the antenna selection functionwhich includes the antenna puncturing. That is, for each subcarrier, thebeamforming logic 112 can direct the symbols from the three spatialstreams to three or less of the transmit antennas 114, 116, 118, 120,122, based on control information. In one possible approach, the samethree antennas may be used for each of the subcarriers in the system,but some of the subcarriers can also contain antenna puncturing forthese three antennas. In another approach, a different combination oftransmit antennas (from 1 to 3 antennas each) may be selected from theavailable 5 for each subcarrier in the system. Using this approach, all5 of the antennas may be used during a transmission, but only a maximumof three antennas will be used per subcarrier.

In at least one embodiment, the beamforming logic 112 may simplymultiply a column vector of input symbols for a particular subcarrier bya beamforming matrix to achieve a vector of output symbols for thesubcarrier. The output symbols may then be distributed to theappropriate mapper/inodulators. For example, if antennas 114, 116, and118 were selected for a subcarrier, without any puncturing, then thefollowing beamforming matrix may be used:

$W = \begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\0 & 0 & 0 \\0 & 0 & 0\end{bmatrix}$

If antennas 114, 116, and 118 are selected for the subcarrier andantenna 116 is to be punctured, then the following beamforming matrixmay be used:

$W = \begin{bmatrix}1 & 0 & 0 \\0 & 0 & 0 \\0 & 0 & 1 \\0 & 0 & 0 \\0 & 0 & 0\end{bmatrix}$

and so on. As before, the control information may be generated, invarious embodiments, within the receiving device, in the transmittingdevice itself, or in some other location.

In the transmitter system 110 of FIG. 7, each of the available transmitantennas 114, 116, 118, 120, 122 has a dedicated transmit chain 124associated with it. To reduce implementation costs, it may be desirableto reduce the number of transmit chains 124 to equal the number ofspatial streams. An antenna switch may then be used to select an antennafrom the available antennas for each of the spatial streams. FIG. 8 is ablock diagram illustrating an example antenna switch arrangement 130 inaccordance with an embodiment of the present invention. The switcharrangement 130 may be used, for example, with the system 50 of FIG. 5when the number of available antennas exceeds the number of spatialstreams. As shown, the switch arrangement 130 includes multiple transmitchains 132, 134, 136 and an antenna switch 138. The number of transmitchains 132, 134, 136 is equal to the number of spatial streams beingused. The antenna switch 138 is coupled to a plurality of antennas 140,142, 144, 146, 148. As shown, the number of antennas (i.e., 5 in theillustrated embodiment) is greater than the number of transmit chains(i.e., 3 in the illustrated embodiment). The antenna switch 138 isoperative for controllably coupling the output of each transmit chain132, 134, 136 to an antenna selected for the corresponding spatialstream. The antenna switch 138 may receive control signals thai identifyhow the connections are to be made. Antenna puncturing may be applied inthe antenna puncture logic 68 (see FIG. 5).

In at least one embodiment of the invention, the antenna puncturingdetermination is performed using an exhaustive search approach. First,all of the antenna selection possibilities are determined, assumingantenna puncturing may be used. For each possibility, a performancemetric may then be calculated (e.g., the Shannon capacity of thechannel, etc.). The antenna selection possibility that results in thehighest performance metric value may then be chosen for a subsequenttransmission. Other techniques may alternatively be used.

FIG. 9 is a flowchart illustrating an example method 160 for performingantenna puncturing in accordance with an embodiment of the presentinvention. The method may be implemented within, for example, aMIMO-enabled device or system that is implementing spatial multiplexing.First, input data is divided into N spatial streams (block 162). Anynumber of spatial streams (two or more) may be used to perform spatialmultiplexing. The data symbols in the spatial streams are then assignedto subcarriers of a multicarrier (e.g., OFDM) band (block 164). At atransmit time, for some of the subcarriers, the symbols in the spatialstreams will be transmitted from N transmit antennas. That is, for thesesubcarriers, no antenna puncturing is performed. For at least onesubcarrier, however, symbols are transmitted from less than N transmitantennas at the transmit time (block 166). This subcarrier has thusundergone antenna puncture. An example of this is shown in FIG. 4, wheresubcarriers 1, 3, 4, 6, 7, and 8 have undergone antenna puncture, whilesubcarriers 0, 2, and 5 have not. The antenna puncturing may beperformed in response to control information. The control informationmay be generated remotely (e.g., in a remote receiving device, etc.) orlocally (e.g., within the transmitting device itself). Antennapuncturing may not need to be performed for every transmit time.

In the discussion above, antenna puncturing is described in the contextof physical transmit antennas. However, in at least one embodiment ofthe present invention, antenna puncturing is used in connection with“virtual antennas.” The term “virtual antennas” refers to output probesthat are connected to the physical antenna by some fixed combiningmatrix so that the generated signal is obtained by:

x=FWs

where F is a fixed matrix (e.g., the discrete Fourier transform matrix,etc.), W is the antenna puncturing matrix, and s is the vector ofspatially expanded symbols. A more detailed description of virtualantennas can be found in “Description and Link Simulations of MIMOSchemes for OFDMA based E-UTRA Downlink Evaluation,” 3GPP R1-050903,Qualcomm Europe, which is hereby incorporated by reference.

The techniques of the present invention are not limited to use withinwireless systems. Applications within wired system also exist. Forexample, in at least one embodiment, puncturing techniques are usedwithin a digital subscriber line (DSL) or asymmetrical digitalsubscriber line (ADSL) system.

The techniques and structures of the present invention may beimplemented in any of a variety of different forms. For example,features of the invention may be embodied within laptop, palmtop,desktop, and tablet computers having wireless capability; personaldigital assistants (PDAs) having wireless capability; cellulartelephones and other handheld wireless communicators; pagers; satellitecommunicators; cameras having wireless capability; audio/video deviceshaving wireless capability; network interface cards (NICs) and othernetwork interface structures; base stations; wireless access points;integrated circuits; as instructions and/or data structures stored onmachine readable media; and/or in other formats. Examples of differenttypes of machine readable media that may be used include floppydiskettes, hard disks, optical disks, compact disc read only memories(CD-ROMs), digital video disks (DVDs), Blu-ray disks, magneto-opticaldisks, read only memories (ROMs), random access memories (RAMs),erasable programmable ROMs (EPROMs), electrically erasable programmable,ROMs (EEPROMs), magnetic or optical cards, flash memory, and/or othertypes of media suitable for storing electronic instructions or data. Asused herein, the term “logic” may include, by way of example, softwareor hardware and/or combinations of software and hardware.

It should be appreciated that the individual blocks illustrated in theblock diagrams herein may be functional in nature and do not necessarilycorrespond to discrete hardware elements. For example, in at least oneembodiment, two or more of the blocks in a block diagram are implementedin software within a digital processing device. The digital processingdevice may include, for example, a general purpose microprocessor, adigital signal processor (DSP), a reduced instruction set computer(RISC), a complex instruction set computer (CISC), a field programmablegate array (FPGA), an application specific integrated circuit (ASIC),and/or others, including combinations of the above. Hardware, software,firmware, and hybrid implementations may be used.

In the foregoing detailed description, various features of the inventionare grouped together in one or more individual embodiments for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimed inventionrequires more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive aspects may lie in less thanall features of each disclosed embodiment.

Although the present invention has been described in conjunction withcertain embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art readily understand.Such modifications and variations are considered to be within thepurview and scope of the invention and the appended claims.

1. A method comprising: splitting input data into N spatial streams toperform spatial multiplexing MIMO, where N is a positive integer greaterthan one; for each spatial stream, assigning data symbols to datasubcarriers of a multicarrier band; and at a transmit time, transmittingdata symbols from N transmit antennas for some data subcarriers in saidmulticarrier band and transmitting data symbols from less than Ntransmit antennas for at least one other data subcarrier in saidmulticarrier band, in response to control information, whereintransmitting data symbols from less than N transmit antennas for atleast one other subcarrier is performed to increase channel capacity ina corresponding MIMO channel.
 2. The method of claim 1, wherein: saidcontrol information is received from a remote receiving device beforesaid transmit time.
 3. The method of claim 2, wherein: said remotereceiving device generates said control information based on, amongother things, channel information for said MIMO channel.
 4. The methodof claim 1, further:comprising: said control information is generatedlocally before said transmit time.
 5. The method of claim 1, wherein:transmitting data symbols from N transmit antennas for some subcarriersincludes transmitting data symbols from N transmit antennas for a firstsubcarrier that has been assigned a total transmit power of Pa, whereina power level of Pa/N is transmitted from each of said N transmitantennas for said first subcarrier; and transmitting data symbols fromless than N transmit antennas for at least one other subcarrier includestransmitting data symbols from L transmit antennas for a secondsubcarrier that has been assigned a total transmit power of P_(b), whereL is less than N, wherein a power level of P_(b)/L is transmitted fromeach of said L transmit antennas for said second subcarrier.
 6. Themethod of claim 1, wherein: said transmit antennas are virtual antennas.7. An apparatus comprising: a spatial stream interleaver to generate Nspatial streams from input data, where N is a positive integer greaterthan one, said N spatial streams for use in performing spatialmultiplexing MIMO; a subcarrier assignment function for each of said Nspatial streams to assign symbols from the spatial stream to datasubcarriers of a multicarrier band; and antenna puncture logic toperform antenna puncturing for said N spatial streams so that datasymbols are transmitted from N transmit antennas for some datasubcarriers of said multicarrier band and data symbols are transmittedfrom less than N transmit antennas for at least one other datasubcarrier of said multicarrier band at a particular transmit time,wherein said antenna puncture logic performs said antenna puncturing toincrease capacity in a corresponding MIMO channel.
 8. The apparatus ofclaim 7, wherein: said antenna puncture logic performs said antennapuncturing in response to control information, wherein said controlinformation is received from a remote receiving device.
 9. The apparatusof claim 7, wherein: said antenna puncture logic performs said antennapuncturing in response to control information, wherein said antennapuncture control information is generated locally based on channelinformation.
 10. The apparatus of claim 7, wherein: said subcarrierassignment function includes a serial-to-parallel converter.
 11. Theapparatus of claim 7, wherein: said transmit antennas are virtualantennas.
 12. The apparatus of claim 7, wherein: when data symbols aretransmitted from less than N transmit antennas for a first subcarrier,an assigned power for said first subcarrier is divided equally amongsaid less than N transmit antennas.
 13. An article comprising a storagemedium having instructions stored thereon that, when executed by acomputing platform, operate to: split input data into N spatial streamsto perform spatial multiplexing MIMO, where N is a positive integergreater than one; for each spatial stream, assign data symbols to datasubcarriers of a multicarrier band; and at a transmit time, transmitdata symbols from N transmit antennas for some data subcarriers in saidmulticarrier band and transmit data symbols from less than N transmitantennas for at least one other data subearrier in said multicarrierband, in response to control information, wherein operation to transmitdata symbols from less than N transmit antennas for at least one othersubcarrier is performed to increase channel capacity in a correspondingMIMO channel.
 14. The article of claim 13, wherein: said controlinformation is received from a remote receiving device, before saidtransmit time.
 15. The article of claim 14, wherein: said remotereceiving device generates said antenna puncture control informationbased on, among other things, channel information for said correspondingMIMO channel.
 16. The article of claim 13, wherein: said controlinformation is generated locally, before said transmit time.
 17. Asystem comprising: a plurality of dipole transmit antennas; a spatialstream interleaver to generate N spatial streams from input data, whereN is a positive integer greater than one, said N spatial streams for usein performing spatial multiplexing MIMO; a subcarrier assignmentfunction for each of said N spatial streams to assign symbols from thespatial stream to data subcarriers of a multicarrier band; and antennapuncture logic to perform antenna puncturing for said N spatial streamsso that data symbols are transmitted from N transmit antennas for somedata subcarriers of said multicarrier band and data symbols aretransmitted from less than N transmit antennas for at least one otherdata subcarrier of said multicarrier band at a particular transmit time,wherein said antenna puncture logic performs said antenna puncturing toincrease capacity in a corresponding MIMO channel.
 18. The system ofclaim 17, wherein: said antenna puncture logic performs said antennapuncturing in response to control information, wherein said controlinformation is received from a remote receiving device.
 19. The systemof claim 17, wherein: said antenna puncture logic performs said antennapuncturing in response to control information, wherein said antennapuncture control information is generated locally based on channelinformation.
 20. The system of claim 17, wherein: said plurality ofdipole transmit antennas includes more than N dipole transmit antennas.